This type of apparatus, called a mixer, is generally used in the wood-processing industry and other chemical industries for mixing various fluids with each other and for mixing solid materials with fluids. These devices are constructed with the object of achieving the greatest possible mixing efficiency with the lowest possible power consumption. Another object is to construct the equipment so that the greatest possible reliability of operation is achieved and that the maintenance or replacement of the shaft sealing and bearing parts may be effected without the necessity of emptying the mixing tank.
In general, the known mixers are inserted into the mixing tank from the side thereof and the reach of the mixing member, such as a mixing blade or propeller, inside the tank is fairly short. The shaft is supported by sealings and bearings at a point which is relatively far from the point of loading caused by the mixing member. In other words, in heretofore known mixers, the shaft has been supported either entirely outside the tank or at least closely adjacent to the wall thereof mainly to facilitate repairs as needed. This, however, necessitates the use of a large diameter mixer shaft to minimize deflections caused by various strains. Consequently, large shaft sealings are needed and, despite the thickness of the shaft, deflections of the shaft which are harmful to the sealing still occur.
An example of the mixer essentially as described above is found in German Patent DE 31 50 537 which discloses an arrangement in which the mixer is mounted on a flange at the wall of the mixing tank so that the entire mixing unit can be removed from the tank. One of the major disadvantages of the apparatus in accordance with that publication, however, is that the mixer cannot be entirely removed unless the mixing tank is emptied at least down to the lower edge of the opening through which it is inserted. A further drawback is the large diameter of the shaft for preventing deflections of the shaft and other stresses to which the bearing system and sealings are subjected.
U.S. Pat. No. 3,539,155 discloses a mixing tank which is entirely closed and in which the mixer is driven by powerful magnets through the cover of the tank. A tapered shell is provided around the mixer shaft and the bearings are arranged both next to the mixing members and close to magnet switch. Although proper support for the mixing shaft has thus been provided, the service of the apparatus has not been given any consideration. Since the mixer is installed in the cover of the mixing tank, the entire mixer can be removed from the tank without emptying the tank contents prior thereto. This arrangement, however, is not possible if the mixer is installed in a sidewall of the tank. In this case, a great number of different factors have to be taken into account, starting from the shaft being deflected by gravity and including numerous sealing problems which occur both during the operation and the service of the apparatus. None of these problems have been considered or addressed in the known prior art publications. In many cases, however, there is also no choice of location of the mixer relative to the mixing tank but the mixer must be disposed at the side of the tank irrespective of the problems caused thereby.
In some installations where the mixer is located at the side of the mixing tank, service of the mixer has been performed successfully by providing the mixer shaft with an additional sealing which can be closed off during service. In that case, it is possible to replace the shaft sealing if the sealing is of a replaceable type. Bearings and sealings that cannot be disassembled may be replaced in some types of shafts by dismantling all drive equipment and support structures of the bearings and by temporarily supporting the shaft.